Alcohol Moiety-Tethering Acylazides as Versatile Isocyanate Precursors for Polymerization Initiators and Monomers

Polyurethane-Type Poly[3]rotaxanes Synthesized from Cyclodextrin-Based [3]Rotaxane Diol and Diisocyanates

Synthesis of polyurethane-type poly[3]rotaxanes is achieved by polyaddition between a cyclodextrin (CD)-based [3]rotaxane diol and various diisocyanate species, which provide a more defined structure compared to conventional polyrotaxane syntheses. In this study, hydroxyl groups on CDs of [3]rotaxane diol are initially acetylated, and deprotected after the polyaddition to introduce polyurethane backbone structure into polyrotaxane framework. Despite a relatively complicated chemical structure, [3]rotaxane diol monomer is successfully synthesized in a high yield (overall 67%) without any taxing purification process, which is beneficial for practical applications. The polymerization itself proceeds well under a standard polyaddition reaction condition to afford corresponding polyurethanes around 80% yield with Mn > 30 kDa. The poly[3]rotaxanes show different aggregation behavior or optical properties, whether or not acetyl groups are present, and are analyzed by XRD, SEM, and fluorescence measurements.

Click to Self-immolation: A "Click" Functionalization Strategy towards Triggerable Self-Immolative Homopolymers and Block Copolymers

Self-immolative polymers (SIPs) are a class of degradable macromolecules that undergo stimuli-triggered head-to-tail depolymerization. However, a general approach to readily end-functionalize SIP precursors for programmed degradation remains elusive, restricting access to complex, functional SIP-based materials. Here we present a "click to self-immolation" strategy based on aroyl azide-capped SIP precursors, enabling the facile construction of diverse SIPs with different trigger units through a Curtius rearrangement and alcohol/thiol-isocyanate "click" reaction. This strategy is also applied to polymer-polymer coupling to access fully depolymerizable block copolymer amphiphiles, even combining different SIP backbones. Our results demonstrate that the depolymerization can be actuated efficiently under physiologically-relevant conditions by the removal of the trigger units and ensuing self-immolation of the p-aminobenzyl carbonate linkage, indicating promise for controlled release applications involving nanoparticles and hydrogels.

Aggregation Behavior of Cyclodextrin-Based [3]Rotaxanes

The aggregation of a cyclodextrin (CD)-based [3]rotaxane has been observed and analyzed in detail for the first time in this work. Although the hexagonal packing aggregation of CD-based polyrotaxane is a well known phenomenon, corresponding studies in terms of rotaxanes without any polymer structure have not been conducted so far, probably owing to the difficulty of the molecular design. We synthesized a series of [3]rotaxane species by using a urea-end-capping method and evaluated their aggregation behavior by XRD and SEM measurements. [3]Rotaxane species containing native CD rings showed clear signals assigned to the hexagonal packing by XRD measurement as did polyrotaxane; this proved their aggregation capability. Because the corresponding per-acetylated derivatives did not show this aggregation behavior, the driving force of this aggregation was suggested to be hydrogen bond formation among CD units. The effect of axle end structures and partial acetylation of CDs were also studied.

Intermolecular Interactions and Spectroscopic Signatures of the Hydrogen-Bonded System-n-Octanol in Experimental and Theoretical Studies

n-Octanol is the object of experimental and theoretical study of spectroscopic signatures and intermolecular interactions. The FTIR measurements were carried out at 293 K for n-octanol and its deuterated form. Special attention was paid to the vibrational features associated with the O-H stretching and the isotope effect. Density Functional Theory (DFT) in its classical formulations was applied to develop static models describing intermolecular hydrogen bond (HB) and isotope effect in the gas phase and using solvent reaction field reproduced by Polarizable Continuum Model (PCM). The Atoms in Molecules (AIM) theory enabled electronic structure and molecular topology study. The Symmetry-Adapted Perturbation Theory (SAPT) was used for energy decomposition in the dimers of n-octanol. Finally, time-evolution methods, namely classical molecular dynamics (MD) and Car-Parrinello Molecular Dynamics (CPMD) were employed to shed light onto dynamical nature of liquid n-octanol with emphasis put on metric and vibrational features. As a reference, CPMD gas phase results were applied. Nuclear quantum effects were included using Path Integral Molecular Dynamics (PIMD) and a posteriori method by solving vibrational Schrödinger equation. The latter applied procedure allowed to study the deuterium isotope effect.